The present invention relates to packaging of stacks of multiply paper articles or the like, by wrapping each stack, or two or more stacks, with a heat-weldable wrapping sheet folded around the stack and welded along overlapped areas, so as to define a wrapping.
The articles can be of different type, e.g. folded handkerchiefs of elastic tissue, paper napkins, of one or more layers, smooth, creased, padded, etc.
Machines for packaging stacks of multiply paper articles or the like, by wrapping each stack, or two or more stacks, with a heat-weldable wrapping sheet folded around the stack and welded along overlapped areas, typically include:
a first line for conveying stacks of articles
a second line for feeding the wrapping sheets, which, in a working station, places and maintains each sheet, so that it is kept dwelling in vertical position;
a third line arranged perpendicular to the first line, from which the third line is fed stepwise and crosswise to said working station, so that each stack gets engaged with a wrapping sheet, for packaging the stacks into a respective wrappings.
In the packaging line, the stack engages the sheet, which is pulled thereby and, in cooperation with suitable means, folded around the stack, so as to take a substantially sleeve-like shape with the edges overlapped and subsequently welded.
The heads of the sleeve are first folded onto the front and rear facings of the stack and then welded to define the stack wrapping.
The wrapping sheets are usually made of polypropylene, whose rigidity is comparable with paper rigidity, so positioning and forwarding sheets in horizontal or vertical position does not cause particular problems, taking into consideration the techniques currently used.
However, it is to be noted that the cost of polypropylene increases considerably the cost of the package.
From the economic point of view, polythene is advisable, though its flexibility causes big difficulties to its moving, obtained by mechanical means, and/or positioning; therefore the its current use is not significant.
In a known machine, the second line includes a reel, situated upstream the line, from which continuous film is drawn stepwise, to obtain wrapping sheets.
Each sheet is conveyed and kept in the working station by strip-like belts connected functionally to vacuum means.
The second line includes two endless conveyors, situated one over the other downstream of the working station, with their runs facing each other.
The vacuum means keep steady the sheet in said working station until it is hit by a stack and clamped between the said opposite runs of the endless conveyors, which allows deactivation of the vacuum means.
It is to be noted that anticipated deactivation of the vacuum means with respect to the clamping makes the sheet fall, while a late deactivation stretch the sheet, which is kept by the vacuum on one side, and pushed by the stack on the other.
Taking into consideration the elasticity and inertia of the used fluid, i.e. air, technical-functional complications are evident.
The above described technical solution does not allow rapid adaptation of the machine to any size change.
According to another known machine, strip-like belts are used to place the sheet in the working station.
The sheet is cut from the film when it is clamped between an already packaged stack, situated downstream of the working station, and a stack to be packaged, situated upstream.
The strip-like belts are disengaged from the edges of the sheet in time relation with what has been said above.
In both known machines, the film is delivered by the relative reel in a discontinuous way, which causes alternating acceleration and deceleration resulting in pulling and releasing of the film.
The film, with ornaments and/or information about the product to be packaged, is often shifted, which can result in undesired offsets of the writings with respect to the article.
This disadvantage can be limited by setting the reel at high level, i.e. as close as possible to the film cutting station, or by using suitable actuators, connected to sensors, which reset the predetermined position of the wrapping sheet.
The known machines are complicated and expensive, and their efficiency is limited due to the strict inter-relation between the film cutting and the sheet keeping action in the working station.
The object of the present invention is to avoid the above mentioned disadvantages by a machine, whose working station receives, locates and keeps each wrapping sheet in a rapid and efficient way, no matter of the stack size, of the material of the wrapping sheet and of the number, i.e. two or more, of stacks of articles being packaged arranged side by side.
Another object of the present invention is to propose a machine, in which the wrapping sheet is kept in the working station not only by vacuum means.
A further object of the present invention is to propose a machine which avoids curling or stretching of the wrapping sheet during its wrapping around the stack.
A still further object of the proposed machine is to give perfectly calibrated, although semi-rigid, packages.
A yet further object of the present invention is to propose a machine, in which operation speed of the stacks feeding line depends on the working means of the packaging line, cooperating with the working station, and in which the feeding line deactivates means for pulling the stacks, if these means are stressed in an anomalous way.
The above mentioned objects are obtained, in accordance with the contents of the claims, by a machine for packaging stacks of multiply articles of paper or the like, into wrappings obtained by wrapping sheets, the machine including:
a first line for conveying and separating stacks of multiply articles of paper;
a working station for wrapping stacks of multiply articles of paper;
a second line for feeding stepwise heat-weldable wrapping sheets to the working station, each sheet being placed and kept vertically in a waiting position in the working station;
a third line (3) including an upstream section fed stepwise with stacks by the first line, and passing crosswise through the working station, the third line moving at least one stack
towards the sheet, so that the sheet gradually folds around the stack or stacks longitudinal contour while overlapping parallel edges of the sheet are heat-welded;
said second line further including:
first means and second means designed for receiving a wrapping sheet from conveying means situated upstream, for pulling said sheet to said working station, for clamping said sheet in said working station in at least one upper area;
keeping means cooperating with said first means to allow said sheet to pass through said working station and to be stabilized while dwelling therein.